PATTERNS IN DISTRIBUTION AND ABUNDANCE OF A ...

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NONCOEVOLVED ASSEMBLAGE OF ESTUARINE FISHES IN CALIFORNIA. PETER B. MOYLE,l ROBERI' A. DANIELS," BRUCE HERBOLD,l. AND DONALD ...
PATTERNS IN DISTRIBUTION AND ABUNDANCE OF A NONCOEVOLVED ASSEMBLAGE OF ESTUARINE FISHES IN CALIFORNIA PETER B. MOYLE,l ROBERI' A. DANIELS," BRUCE HERBOLD,l AND DONALD M. BALTZ·

ABSTRACT The patterns of distribution and abundance of the fishes of Suisun Marsh, a portion of the SacramentoSan Joaquin estuary in central California, were studied over a 54-month period. Thtal fish abundance in the marsh exhibited strong seasonality; numbers and biomass were lowest in winter and spring and highest in late summer. Freshwater inflow was highest in the winter and lowest in late summer, when salinities and temperatures were highest. 'I\venty-one species were collected on a regular basis; the 10 most abundant were MO'1'()lle saxatilis, Pogonichthys macrolepidotus, GasterostellS aculeat"IS, Hystel'ocarpllS

Itw'II~ysis mercedis abundance rankings are described in text.

flow, indicating that catches were highest in late summer and lowest in early spring. However, when the patterns of occurrence of the 12 most abundant species were examined, three groups appeared: resident species. winter seasonals, and spring/summer seasonals. The "resident species" included the native splittail, tule perch, Sacramento sucker, prickly sculpin, and threespine stickleback as well as the introduced striped bass, carp, and yellowfin goby. 1Wo additional 110

NEOt1YSIS

I 3 N

D

E X 2

species, native white sturgeon and introduced American shad, probably also belonged in this category, as they were caught at all times of the year but too infrequently to draw any firm conclusions. Splittail. striped bass. tule perch, Sacramento sucker, carp, and yellowfin goby had similar patterns of abundance (Figs. 4, 5) and were correlated (P < 0.05) with each other and with total biomass, numbers, and species (Thbles 3, 4). All six species usually became more abundant in our catches as the sum-

MOYLE ET AL.: NONCOEVOLVED ASSEMBLAGE OF ESTUARINE FISHES

TABLE 4.-Spearman rank correlation among species ranked by month (lower matrix) by numbers and among environmental and other variables ranked by month (upper matrix). Underlined values are significant at P > 0.05. 2

4

3

5

S

7

8

9

10

11

12 Month series Temperature Salinity Secchi depth Outflow Neomysis Crangon Palaemon Numbers! trawl 0.51 10. Gramsltrawl 0.74 11. Speciesltrawl 12. Diversity (H') 0.07

13. 14. 15. 16. 17. 18. 19. 20. 21.

Striped bass Splittail 0.50 Tule perch 0.44 Sacramento sucker 0.19 Vellowlin goby 0.68 Carp 0.46 Prickly sculpin -0.14 Stickleback -0.41 Delta smelt -0.11

-0.15 -0.54 -0.10 0.43 0.14 - 0.04 - 0.04 - 0.51 - 0.79 - 0.80 - 0.64 -0.19 0.44 0.33 0.30 0.37 0.05 0.27 0.19 -0.62 -0.29 0.42 0.32 0.48 0.37 0.39 0.07 0.38 0.46 -0.78 -0.55 0.01 -0.11 -0.19 0.54 -0.13 -0.43 0.04 -0.24 0.01 0.51 0.58 0.32 0.22 0.51 -0.52 -0.41 - 0.58 - 0.34 - 0.51 -0.06 --0.56 -0.32 -0.14 -0.03 -0.10 0.16 0.53 0.38 0.46 0.35 0.13 -0.13 0.34 0.06 0.11 0.34 0.09 -0.19 0.25 0.01 0.12 0.04 0.15 -0.05 -0.09 0.05 0.07 -0.22 -0.17 0.09 0.03 -0.05 -0.15 -0.15 0.40 0.55 0.56 -0.08 0.08 0.21

22. 23. 24. 25.

Longfin smelt Threadfin shad Staghorn sculpin Starry flounder

-0.01 -0.09 -0.12 0.21 -0.38 -0.15 -0.04 -0.02 0.38 0.00 -0.24 -0.11 -0.47 0.42 -0.13 -0.05 0.06 - 0.06 - 0.02 0.20 0.18 0.30 0.03 0.30 0.18 -0.14 0.25 0.22

-0.07 -0.17 -0.24 -0.09 13

14

15

16

17

"EAN BIOMASS PER TRA.UL

MEAN NUMBEP

or

FISH PER TRAUL

30

!m r

I

I S H

10

1979

FIGURE

1~80

1981

1982

1983

3.-1rends in mean numbers and grams of fish per trawl.

18

19

20

0.43 0.36 0.17 0.10

0.21 0.30 0.37

0.69 0.01 0.00

21

22

23

1. 2. 3. 4. 5. 6. 7. 8. 9.

24

mer progressed although the two introduced species, striped bass and yellowfin goby, tended to peak later than the other species. Consequently, they all showed significant (P < 0.05) negative correlations with outflow. All except Sacramento sucker and tule perch had significant positive correlations with salinity and temperature. There was a general decline in fish abundance throughout the 5-yr period. This was reflected in that four of the six species showed a positive correlation with species diversity, and all had a negative correlation with month series. Prickly sculpin seemed to peak in abundance earlier in the year than the first six species (Fig. 4) but the pattern was obscured by the considerable year-to-year variation in abundance of young-of-year fish. Adults were resident in the marsh but appeared in the trawls on an irregular basis because of their tendency to hide under logs and other objects (Moyle 1976). Overall, prickly sculpin had negative correlations with salinity and Secchi depth, but positive correlations with temperature, N. me1'cedis abundance, and species diversity (Table 3). Threespine stickleback abundance had a negative correlation only with temperature, presumably because their reproductive behavior obscured our ability to catch them. They were most abundant in the trawls in February through May, and the catch consisted primarily of gravid females and schools of youngof-year fish. The males were apparently defending their nesting territories in emergent vegetation. By late summer sticklebacks were rare in the trawls but could be taken in seine hauls made through weedy areas. The "winter seasonals" were three plankton-

111

FISHERY BULLETIN: YOLo 84. NO.1 PRICklY SCULPIN

TULE PERCH

P 4

~j

P

[

E

R

R

"

"

4

I N U 2 1

I N U 2 1 E

[

SACRAMENTO SUCKER

c



SPLITTAIL

lJl

10

B

8

1 (

H

"I

4

N U

1 E

1979

FIGURE

1988

1981

1982

1983

1988

1981

1982

1983

4.-Capture rates of native resident species within Suisun Marsh. Mean catch per effort is described as percent of the total catch for each species.

feeding species, delta smelt (native), longfin smelt (native), and threadfin shad (introduced). All three species tended to be most abundant in November through January, although the pattern was not always consistent (Fig. 6). Threadfin shad were the most erratic of the three species in abundance; they were especially abundant in the summer of 1981. Longtin smelt were largely absent from our samples in 1979 and 1981. Delta smelt abundance was positively correlated (P < 0.05) with that of the other two species, although the correlation between longfin smelt and threadfin shad was not significant. All three species had negative correlations with temperature, and positive correlations with Secchi depth. The "spring/summer seasonals" were staghorn sculpin and starry flounder, both euryhaline marine species that were represented mainly by young-ofyear. Their patterns of abundance were not consistent (Fig. 6) and the peaks occurred anytime from March through September. Consequently, staghorn 112

1979

sculpin did not show any significant correlations with the environmental variables, although starry flounder did show negative correlation with Secchi depth. Both species had a positive correlation with species diversity, presumably because they were rare in our samples during the last 2 years when the marsh was dominated by freshwater. In addition to the 12 species that appeared regularly in our trawls, there were a number of other species of potential importance to the fish community that were either not sampled adequately by the trawl or were absent because of the effects of the 1976-77 drought. Five species that were not sampled adequately were inland silverside, chinook salmon, Sacramento squawfish, mosquitofish, and rainwater killifish. The silversides were abundant year around in the shallow, sandy or weedy areas found in some sloughs. Silversides appeared in seine hauls in 20 of the 22 mo in which seining was done; they were generally the most abundant fish in these hauls. Juvenile chinook salmon and squawfish were com-

MOYLE ET AL.: NONCOEVOLVED ASSEMBLAGE OF ESTUARINE FISHES

mon in the marsh in February, March, and April (times of high outflows) and were taken mainly in seines. The tendency of the salmon to remain close to the banks and vegetation and to get sucked into

YELLOlJr IN GOB"'

12

diversions of marsh water consequently has led to the screening of one major diversion in the marsh. Squawfish were abundant in the Sacramento River and juveniles are known to disperse widely during high flows (Smith 1982). Mosquitofish and rainwater killifish were present in ponds adjacent to the sloughs, along with silversides and sticklebacks; mosquitofish were planted in some areas for mosquito control.

Principal Components' Analysis The peA using the numbers per trawl matrix resulted in four components that explained 47% of the variance in the matrix (Table 5). The first component loaded most heavily on tule perch, Sacramento sucker, and splittail, native resident species most abundant in dead-end sloughs. and to a lesser extent on carp and threadfin shad, introduced species common in such sloughs. The second component loaded heavily on striped bass, yellowfin goby, and carp, three introduced species resident throughout the marsh but most frequently captured in the main sloughs; all reached peaks of abundance in late summer. The third component loaded most heavily on prickly and staghorn sculpins, two benthic species that peaked in abundance during the summer months but were relatively scarce during the last 2

B

"~

.4

U

T E

CARP

TABLE 5.-Loadings (rotated) of major fish species on four components produced by a principal components analysis of numbers of fish per trawl (n = 1,238). Values over 0.500 are underlined.

1979

19130

1981

198~

1963

5.-Capture rates of introduced species within Suisun Marsh. Mean catch per effort is described as percent of the total catch for each species. FIGURE

Compo- Compo- Component nent nent 1 2 3

Component 4

0.487 0.549 0.058 0.183 -0.124 0.022 0.447 0.403 -0.011 0.827 0.833 0.254 0.090 0.117 0.043 0.637 0.039

0.300 0.100 0.701 0.631 0.029 -0.061 -0.286 0.403 0.660 0.049 -0.036 -0.038 0.043 0.256 0.047 0.197 -0.296

-0.024 0.318 0.078 -0.157 -0.032 -0.027 -0.121 0.166 0.023 0.085 -0.045 0.377 0.780 0.107 0.727 0.341 0.486

-0.149 0.149 -0.073 0.046 0.747 0.734 0.319 -0.084 0.016 -0.102 -0.017 -0.263 -0.077 -0.030 0.118 0.102 -0.147

Eigenvalue

2.826

1.874

1.829

1.391

Cumulative proportion of variance explained

0.200

0.304

0.396

0.472

Splittail adults Splittailjuveniles Striped bass adults Striped bass juveniles Longfin smelt Delta smelt Threadfin shad Common carp Yellowfin goby Tule perch adults Tule perch juveniles Sculpin adults Sculpin juveniles Starry flounder Staghorn sculpin Sacramento sucker Threespine stickleback

113

FISHERY BULLETIN: VOL. 84, NO.1 THP'EAr"F"ItI SHAD

L.ONGFIN SI"IEL. T

c ~

6

C ~

~

I N

~

.2

E

STARRY fLOUNDER

.8

P E R ~

I N

~

.1

E

1979

.988

1981

1982

.983 STAGHORN SCllPIN

1.0

C A

T C H

P • FIGURE 6.-Capture rates of seasonal species within Suisun Marsh. Mean catch per effort for each month described as percent of total for each species.

E R ~

I

...

N

U T E

.2

1979

years of the study. A similar pattern was shown by threespine stickleback, which also had a relatively large positive loading on this component. The fourth component loaded heavily on delta and longfin smelt, and to a lesser extent on threadfin shad. This is the winter seasonal group identified in the previous analysis. 114

'988

1981

'982

1983

DISCUSSION During the 5-yr study period, the fish assemblage of Suisun Marsh had the following characteristics: 1. There was a strong seasonal pattern of total fish

MOYLE ET AL.: NONCOEVOLVED ASSEMBLAGE OF ESTUARINE FISHES

abundance with numbers and biomass lowest in winter and spring and highest in late summer. Fishes were least abundant when river outflows were highest and most abundant when salinities and temperatures were highest. 2. There was an overall decline in fish abundance and species diversity through the study period. 3. Of the 21 species that occurred in the marsh on a regular basis, 14 were residents, 4 were winter seasonals, and 3 were spring/summer seasonals. Another 21 species occurred sporadically, in small numbers. These were mainly marine and freshwater species that presumably could become established in the marsh if environmental conditions changed significantly. 4. The abundant resident species fell into two groups, one made up of native species that concentrated in the small dead-end sloughs and the other a mixture of introduced and native species that were widely distributed in the marsh, but most abundant in the larger sloughs. 5. The structure of the fish assemblage (i.e., the pattern of distribution and abundance) was fairly consistent over the 54-mo period. The seasonal pattern of fish abundance was due to a number of factors, most importantly 1) variation in sampling efficiency, 2) influxes of young-ofyear fish, 3) favorable environmental conditions for most fish species in late summer, and 4) abundance of Neomysis mercedis. When outflows were high, water levels in the marsh were high and showed little tidal fluctuation. Therefore trawling was less efficient because there was more water and more flooded vegetation available as cover for fish. However, even under these conditions most of the sampling areas were rarely more than 2 m deep, so our trawl covered at least half the water column, and large catches were common, especially early in the study. Therefore, variation in sampling efficiency may have exaggerated the peaks and valleys of the catch curves (Figs. 4, 5) but was unlikely to obscure the general trends in abundance. Probably the most important contributor to the seasonal patterns was the increase in young-of-year striped bass, splittail, prickly sculpin, and tule perch, in June through August These species (and others, to a lesser extent) became vulnerable to our trawl at 30-40 mm SL, and catches of several hundred individuals in a 5-min tow were made on occasion. The rapid growth of these species during summer (Daniels and Moyle 1983; Herbold and Moyle, unpubI. data) indicated that environmental conditions, including warm temperatures and moderate salinities, were favorable for

them and for other euryhaline species (e.g., staghorn sculpin, starry flounder). These same conditions also favored N. me't'cedis, a small shrimp that is an important food item in summer diets of most of the fishes (Herbold fn. 4). It is possible that the summer peak in fish abundance ma,y be due also in part to fishes moving in to take advantage of an abundant food resource. The decline in N. merc.edis abundance in late summer may be related in part to fish predation, although it is presumably related mainly to their seasonal movements within the entire estuary (Orsi and Knutson 1979). The overall decline in fish abundance over the study period seemed to be due to two factors: variation in reproductive success of major species and the fact that 1982 and 1983 were years of unusually high precipitation and runoff, so freshwater conditions prevailed throughout the summer months of both years. Splittail showed an unusually strong year class in 1978, which dominated the 1979, and, to a lesser extent, 1980 samples (Daniels and Moyle 1983). Catches of splittail in 1979 were typically 2-5 times greater than in subsequent years. Striped bass, tule perch, and carp also showed peaks of abundance in 1979 and had low abundances in 1982-83, with one or two peaks of abundance in between. Except for carp, the peaks were largely due to influxes of youngof-year fish. The reason for the abundance of the 1978 year class of fish was presumably related to 1978 being a year of high, but not excessive, outflows. Increased reproductive success during high outflow years has been documented for striped bass (Stevens 1977), splittail (Daniels and Moyle 1983), American shad, chinook salmon, and longfin smelt (Stevens and Miller 1983). However, under extreme outflow conditions (such as e...dsted in 1982 and 1983), youngof-year fish are apparently carried downstream to areas below the marsh (San Francisco and San Pablo Bay) where chances of survival may be less (Stevens 1977). Drought also contributed to the variation in the fish fauna. During 1976 and 1977, severe drought reduced freshwater inflows to the marsh, resulting in sustained high salinities. Freshwater fishes declined dramatically during the drought period (Herrgesell et aI. 1981) and the fishery for catfish (mainly white catfish and black bullhead) was greatly reduced (Baracco 1980). The catfish populations did not recover during the study period, but the regular appearance of young-of-year white catfish in our trawls in late 1983 indicated a recovery may be in progress. Other freshwater fishes found in the marsh (Table 1) showed no signs of increasing. Most were represented in our samples by